Aerodynamic efficiency is something that only applies to time trial athletes, right? From a performance perspective, absolutely not.
More and more, modern-day road racing is becoming more about speed and attention to detail. In the most basic sense, athletes need to be aware of the difference between the common riding positions and the scenarios where aero equipment is favourable. The point of this blog post is to provide the basic knowledge related to the former.
The basics of drag force in cycling
When speed is the key performance outcome measure, it’s power-to-drag that matters most. At speeds above 12.9 km/h, wind resistance exceeds rolling friction and by the time the athlete is travelling at 32.2 km/h, 90% of resistance to forward motion is in the form of aerodynamic drag (Lukes et al., 2005). That means both athlete power output and system coefficient of drag (bike plus rider) are vital performance indicators.
Of the total system coefficient of drag, between 31-39% of aerodynamic drag can be attributed to the bike, with the remaining 61-69% being attributed to the athlete (Lukes et al., 2005). Given the contribution of the athlete to drag force acting on the system, the position of the athlete has the most significant impact on aerodynamic efficiency.
Participant and equipment
Jordy Villani volunteered his time to this round of aero testing. Jordy stands at 186 cm, weighing in at 75 kg, with a system mass of 83 kg. For the testing, Jordy was wearing his basic Cuore skinsuit, Suplest aero shoes and Rule 28 AeroSox. Control wheels were used (HED GT3 and Stinger Disc), limiting the variables contributing to a change in system coefficient of drag. The same testing protocol was used that we used for time trial positioning and the subsequent data was analysed and post-processed in a custom built data analysis package, specific to the application of track aero testing. Jordy’s standard power2max unit was used to collect power data throughout the session, performed at Darebin International Sports Complex (DISC) indoor velodrome.
During the fit process, we often reinforce the primary contact point at the handlebars. Hands on the hoods is the primary contact and indeed, for approximately 90% of your time on the bike, this should be the contact point of choice.
For our road position aero testing, we used this position as our baseline. For Jordy, we were able to determine that his baseline road position coefficient of drag (CdA) was 0.316 m^2.
hands in the Drops or Time Trial Style?
With the front end of a road bike, you have a few options for improving aerodynamic efficiency. The most obvious option is to place the hands in the drops, with the outcome of a reduced torso angle.
Indeed, when we look at the outcome measured on the track, we see a very substantial drop in CdA. For Jordy, there was a 6.3% improvement with an average CdA of 0.296 m^2 recorded.
Want to further improve your speed for a given power output? The other option a rider can take is to keep their hands on the hoods and flatten the forearms. The time trial style position keeps the torso at a similar angle, while reducing the contribution of the forearms to the frontal area of the athlete.
So how much does it matter? Reducing the contribution of the forearms to the frontal area of the athlete has a very substantial impact on aerodynamic efficiency. This position sees a further 4.4% improvement in CdA with a value of 0.282 m^2 recorded.
Hands in the drops provides an impressive improvement in aerodynamic efficiency, equivalent to 24 Watts. If performing a time trial over a 40 km distance, this improvement would translate to a time saving of 72 seconds at 375 Watts.
The use of the time trial style position sees a further improvement in aerodynamic efficiency, equivalent to an additional 16 Watts. While the margin of improvement is less than the initial change, the outcome is no less impressive. Over a 40 km time trial, this improvement would translate to a time saving of 124 seconds over the baseline position, or 52 seconds over the "in the drops" cycling position.
We have provided aero data for the three primary road positions relevant to road cyclists. This information allows the athlete to make an informed decision about something that is incredibly easy to adopt. Equipment choice and position optimisation should reflect the goal of meeting the demands of road cycling. While this is most relevant for the competitive athlete, the concept remains relevant to all road cyclists, from elite to club level athlete and recreational cyclist.
The measured improvements in aerodynamic efficiency come down to a change in torso angle and a change in the angle of the forearms. Lowering the torso and reducing the contribution of the forearms to the frontal area of the athlete both have a significant impact on aerodynamic efficiency.
The data analysis processes would not have been possible without the help of Scott Gigante, creator of the custom data analysis package we use.
Lukes. R.A, Chin. S.B & Haake, S.J 2005, The Understanding and Development of Cycling Aerodynamics, International Journal of Sports Engineering, vol. 8, pp. 59-74. Retrieved from: https://link.springer.com/article/10.1007/BF02844004